Option 1:
Stop playing. Vote with your contribution to the playercount. Some are doing this already. Also, if you’re not playing, you can stop paying if you were omega, and vote with your wallet as well.
Option 2:
When you open the esc menu, there’s the options to log off and to exit the game in the bottom right. On the left side, also at the bottom, are a thumbs up icon, and a thumbs down. If you click the thumbs down icon, the game asks you for more specific feedback, and you can explain that you don’t like photon, or don’t think it’s ready for the removal of an opt out, and provide reasons why you think that.
Option 3:
Support tickets and/or bug reports. For this, you should have specific constructive criticism, not just “wah don’t like gimme back old UI” but explanations of what you want to do, and why photon isn’t up to the required standard to let you do it yet. But it’s a valid method of providing feedback. You can access that on this website, or in-game you can use F12 to bring up the help page and get a link to the support webpage.
Option 4:
The forums. While you’re here already, explain the problems you have with photon. There’s very definitely a CSM who’s been active in this thread, so you might catch his eye if you give useful and reproducible feedback. It’s possible a dev might show up and read some of these comments too.
I’ve been using a combination of these tools myself for various issues, some photon-related, some not. It’s well worth giving them a look. I’m not as aggressively anti-photon after this update as I would have been if they took away the opt out function even as recently as a month go (the last time I tried photon out and conirmed it didn’t feel good enough for me to use yet). As I’ve said previously, I don’t think photon is ready to be live without an opt out yet. But in spite of saying that, I DO think that for me, personally, if we still had an opt out available for photon right now, I wouldn’t be using it because photon is close enough to being where it needs to be, for what I do in-game. It’s not on par with the old UI in a few key areas, and the new features it brings don’t add a lot to my experience, but it’s not bad enough that I find it uncomfortable to use any more. It’s just got a couple of niggling annoyances remaining for me. I can see that other people are more strongly affected by some of the remaining issues though, which is why I say it should still have the opt out at the moment.